Vast Magma Chambers Detected Beneath Mount St. Helens

The 1980 eruption of Mount St. Helens, one of the most active volcanoes in the Pacific Ring of Fire, is famous for its particularly destructive nature. Now, volcanologists at a gathering of the Geological Society of America in Baltimore, Maryland, have announced that, using an advanced detection method, they have found the likely recharge mechanism responsible for setting the events of 1980 in motion, as reported by Science.

Volcanic eruptions release a hell of a lot of energy. Mount St. Helens, a stratovolcano, released at least 100 million billion joules of energy; this total energy release was comparable to the detonation of the largest nuclear warhead ever designed: the Tsar Bomba. Fifty-seven people died when a 360°C (680°F) pyroclastic flow traveling at 1,080 kilometers per hour (670 miles per hour) buried them, and $1.1 billion (£715 million) in infrastructural damage was caused.

This devastating eruption was fueled by a magma chamber beneath the volcano, but the details of its properties have remained sketchy. An international collaborative effort has conceived iMUSH (imaging Magma Under St. Helens), a campaign to use explosives on an unprecedented scale to investigate the plumbing network beneath it.

Researchers planted 2,500 seismometers in the ground around the volcano, which would detect seismic energy waves traveling back and forth through the Earth’s crust. Different wave speeds indicate different densities of materials, so a liquid-solid mixture in a magma chamber would show up differently to solid rock. In order to create these sound waves, 23 explosive shots were detonated at various points nearby, each with the force of a very minor earthquake. By analyzing the seismic wave patterns, the researchers could map the magmatic plumbing system of the crust between 5 and 40 kilometers (3 and 25 miles).

A dual magma chamber system was found: A giant magma chamber at a depth of 5 to 12 kilometers (3 to 7.5 miles) appears to be fed by an even larger one, 12 to 40 kilometers (7.5 to 25 miles) below the surface.

Prior to the 1980 eruption, a series of ascending tremors were detected along a peculiar path, but their point of origin was left unexplained. These tremors are typically emitted by magma moving upwards through the crust, and iMUSH has revealed that it was likely the larger, deeper chamber pumping magma into the shallower chamber, where it pressurized to the point of eruption.

This advanced mapping technique of the magmatic plumbing system should help future volcanologists predict imminent volcanic eruptions. When a similar tremor is heard along the same subterranean path, for example, they could sound the alarm knowing that the volcano is “recharging” for another violent eruption.

“A dual magma chamber is not so surprising,” Professor Steve Sparks, one of the world’s foremost volcanologists but who was not involved in the research, told IFLScience. “The [scientific community] is moving towards the idea of multiple stacked magma bodies through the crust.”

The system beneath Mount St. Helens is not unlike the one recently detected under the Yellowstone caldera in Wyoming, meaning that the same potential warning signal could inform volcanologists of this supervolcano’s impending eruption.